Garry's Mod entity spawner based on random player positions.

sv_entity_spawner.lua

EntitySpawner = EntitySpawner or {} -- Globally accessable table of spawner functions.
local spawnPositions = {}
local spawnDelay = 15
local spawnIterations = 16 -- Can be thought as a time limit: (spawnDelay * spawnIterations) seconds.
local maxAliveEntities = 6
local minAlivePlayers = 5
local enabled = true
local entity = "sent_ball"

if not enabled then return end

function EntitySpawner.Spawn()
    if #ents.FindByClass( entity ) > maxAliveEntities then return end
    local spawnPosition = spawnPositions[ math.random( 1, #spawnPositions ) ]
    if spawnPosition ~= nil then
        local sentEntity = ents.Create( entity )
        sentEntity:SetPos( spawnPosition )
        sentEntity:Spawn()
        sentEntity:PhysWake()
    end
end

function EntitySpawner.Reset()
  table.Empty( spawnPositions )
  timer.Remove( "EntitySpawner" )
end

function EntitySpawner.Initialize()
    for _, player in ipairs( player.GetAll() ) do
        if player:GetObserverMode() == 0 then
            table.insert( spawnPositions, player:GetPos() )
        end
    end
    if #spawnPositions < minAlivePlayers then
        EntitySpawner.Reset()
    else
        timer.Simple( spawnDelay, function() timer.Create( "EntitySpawner", spawnDelay, spawnIterations, EntitySpawner.Spawn ) end )
    end
end

if engine.ActiveGamemode() == "terrortown" then
    hook.Add( "TTTBeginRound", "InitalizeEntitySpawner", EntitySpawner.Initialize )
    hook.Add( "TTTEndRound", "ResetEntitySpawner", EntitySpawner.Reset )
else
    hook.Add( "InitPostEntity", "InitalizeEntitySpawner", function()
        EntitySpawner.Initialize()
        timer.Create( "EntitySpawningRefresher", spawnDelay * spawnIterations, 0, function()
            EntitySpawner.Reset()
            EntitySpawner.Initialize()
        end ) -- Spawner does not have a time limit for non TTT gamemodes, rather spawn positions are refreshed.
    end )
end